As a size of a pattern has rapidly decreased in accordance with miniaturization and high integration of a semiconductor device, a collapse phenomenon of a photoresist pattern has been in the spotlight as the biggest difficulty in a process, and thus, necessarily, a thickness of the photoresist film has gradually decreased in order to have high resolution. However, it has been significantly difficult to etch a layer to be etched with sufficient etch selectivity using a thinned photoresist and a formed pattern, and thus, an inorganic or organic film having high etching resistance has been introduced between the photoresist and the layer to be etched. This film is referred to as a hard mask, and generally, a hard mask process is a process of etching the hard mask using a photoresist pattern to form a pattern and etching the layer to be etched using a pattern of the hard mask. A material of the hard mask used in the hard mask process may be various. For example, polysilicon, silicon nitride, silicon oxynitride, titanium nitride, amorphous carbon, or the like, may be used, and generally, the hard mask is manufactured by a chemical vapor deposition (CVD) method.
The hard mask formed by the chemical vapor deposition method has excellent physical properties in view of etch selectivity or etching resistance, but there are problems such as formation of particles, voids at a portion at which a step is large, and the like. Particularly, high initial equipment investment cost is the point of the matter. In order to solve these problems, there is a need to develop a spin on hard mask composition capable of being easily spin coated using a track coater used in a photo process in a semiconductor line instead of the deposition-type hard mask, and a specific material for the spin on hard mask composition has been developed in earnest. In the case of a hard mask (spin on hard mask) formed through the spin coating, it is difficult to have the same performance as the hard mask through the CVD process in view of etching resistance, but there are advantages in that it may be easy to form a thin film through coating in a solution state, coating uniformity may be improved, and roughness of a surface of the thin film may be decreased, etc. Further, there is an advantage in that initial investment cost is low as compared to the chemical vapor deposition method.
As described above, recently, there is a limitation in implementing fineness of a lithography process in accordance with continuous high integration of a large scale integrated circuit (LSI) even with an existing argon fluoride liquid immersion exposure photoresist, which is the most advanced resist. Particularly, in order to perform a process for an ultra-fine pattern for 30 nm node or less, resolution of a photoresist used in the lithography process serves as a critical and important factor. However, there is a limitation in implementing a pattern of 30 nm or less using the existing photoresist, and in order to solve this problem, a novel additional process has been developed.
As a technology actually applied in a process among various process technologies developed up to now, a double patterning method of performing an exposure process and performing an etching process two times and a double spacer patterning process (SPT) have been mainly used, and a material used for the hard mask in this additional process is commonly referred to as an underlayer film composition. However, a use amount of the underlayer film composition as a novel material for the hard mask has been rapidly increased in a situation in which the underlayer film composition has been used for the hard mask instead of previously used amorphous carbon, and the double patterning process, a process for implementing high resolution, leads the overall ArF lithography process. As the most important physical properties required in the underlayer film as described above, there are excellent coating uniformity in addition to properties such as high etching resistance and heat stability, excellent solubility for a general organic solvent, storage stability, adhesion, and the like. The reason of requiring heat stability is that after forming the underlayer film, a vacuum deposition process is performed thereon at a high temperature as a subsequent process. In general, a low polymer decomposition rate at 400° C. and a film decrease rate of 5% or less are required as heat resistance properties for a stable vacuum deposition process. Etching resistance is another significantly important factor for etching a lower layer with a minimum thickness as the underlayer film. The reason is that the thicker the thickness of the film, the higher the risk that a pattern will naturally fall down during a process. The higher the content of carbon in the polymer, the more advantageous in view of etching resistance, but in consideration of solubility in a solvent and coating uniformity, it is preferable that the content of carbon is 82% or more.
According to the related art, in order to satisfy properties of a material of the underlayer film, as a polymer material in the composition, a polymer having a high content of carbon, high polarity, and high heat stability has been mainly studied. Particularly, various research into polyamide, polyether ether ketone, polyarylether, other phenolic polymers, and the like, has been conducted. It was confirmed that some of the polymers had sufficient high-temperature stability and a film-forming ability. However, when polymers have desired level of carbon contents related with etching resistance, the polymers have problems in view of storage stability, line compatibility, and coating uniformity due to rapid decrease in solubility. When polymers have insufficient heat resistance, the polymers have a problem in that a gas emission amount is large during the process due to low heat stability.
That is, physical properties of the underlayer film composition are dependent on characteristics of the polymer. In particular, heat stability and etching resistance in the characteristics of the polymer are intactly reflected in the characteristics of the underlayer film composition. Heat stability is dependent on stability of a polymer main chain, and the etching resistance is excellent as a carbon content present in the polymer is high. As a polymer having excellent heat resistance, there are polyimide, polyamide, polyaryl ketone ether, and the like, but these polymers have low etching resistance or low solubility in a general organic solvent, such that there is a limitation in using these polymers as a material of the underlayer film.